1. Field of the Invention
The present invention relates to a process for producing a liquid ejection head provided with a piezoelectric body.
2. Description of the Related Art
A piezoelectric type ink jet head provided with a piezoelectric body containing a piezoelectric material such as PZT (Pb(Zr, Ti)O3; lead zirconate titanate) is known. In the piezoelectric type ink jet head, a pressure chamber for applying an ejection pressure to an ink is formed, and an electrode electrically connected to a head substrate is provided on an inner wall surface and an outer wall surface of the pressure chamber. A voltage is applied to the electrode from the head substrate, whereby a side wall, a bottom wall and a top wall of the pressure chamber are deformed to change a capacity of the pressure chamber. An ejection pressure is thereby applied to an ink within the pressure chamber, and an ink droplet is ejected from an ejection orifice communicated with the pressure chamber.
In the production of the piezoelectric type ink jet head, a wiring electrode composed of a metal thin film may be formed on a lateral surface of the piezoelectric body, on which surface the ejection orifice of the pressure chamber is located, in some cases. In this case, it is difficult to form a pattern by an ordinary liquid resist on the lateral surface of the piezoelectric body because the ejection orifice is present, and so a dry film resist is suitably used. In order to prevent pattern defect (abnormality) such as release of the resist, it is important to ensure adhesion between the dry film resist and the piezoelectric body. It is thus conducted to remove air in a vacuum chamber and then bond the dry film resist to the surface of the piezoelectric body under pressure while being heated (vacuum lamination).
In the technology described in Japanese Patent Application Laid-Open No. 2010-181813, a further device is provided for the dry film resist. Specifically, in the dry film resist, a surface roughness Ra of a surface, coming into contact with a resist layer, of a protecting layer laminated on the resist layer (photosensitive resin layer) is controlled to more than 0.5 μm. Irregularities are applied to the protecting layer in this manner, whereby a bubble liable to remain at a contact surface between the protecting layer and the resist layer can be efficiently removed.
However, the dry film resist is relatively good in adhesion to a metal such as Cu or Al, but not very good in adhesion to a piezoelectric body such as PZT. The conventional vacuum lamination technology and the technology described in Japanese Patent Application Laid-Open No. 2010-181813 pay attention to the removal of the bubble and cannot sufficiently ensure adhesion between the dry film resist and the piezoelectric body. In particular, when a pattern is formed on the lateral surface of the piezoelectric body, on which surface the ejection orifice is located, with the dry film resist, pattern release may occur due to insufficient adhesion though the bubble can be sufficiently removed. In fact, when the dry film resist is vacuum-laminated on the ejection orifice of the piezoelectric body, the dry film resist may be pushed into the interior of the pressure chamber through the ejection orifice of the piezoelectric body in some cases. In order to remove the resist pushed into the interior of the pressure chamber by development, a longer development time is required compared with a resist present on a flat portion. However, if the development time is long, a resist portion (resist pattern) intended to remain is also released from the surface of the piezoelectric body to cause pattern defects. It is thus desired to more improve the adhesion between the dry film resist and the piezoelectric body.